From the related art, various micromechanical magnetic field sensors are known, which convert an interaction between an electric current and a magnetic field into a force, based on the Lorentz force acting on electric charges. This force acting on the magnetic field sensor structure causes a deflection, which can be detected by various methods.
To illustrate the related art, first three rocker-shaped sensor structures will be described.
The first known magnetic field sensor structure is a resonant SiO.sub.2 -torsion rocker, as is known from B. Eyre and K. S. J. Pister, Micromechanical Resonant Magnetic Sensor in Standard CMOS, Transducers 97, 1997 Int. Conf. Solid-State Sensors and Actuators, Chicago, Jun. 16-19, 1997.
In this design approach, an aluminum loop is generated on a freely suspended SiO.sub.2 -rocker structure. As a result an electromagnetic excitation (alternating current interacting with the magnetic field) having the mechanical resonant frequency of the vibrator, a mechanical torsional vibration ensues. The amplitude is detected using a piezoresistive Wheatstone bridge circuit. Due to the high attenuation of the structure (SiO.sub.2 --Al), only low qualities (i.e., high attenuation values) are achieved even under vacuum, namely qualities in the range of Q=10. Due to the thin substrates (particularly SiO.sub.2), the rocker structure bends considerably under the action of a force.
The second known magnetic field sensor structure is a resonant monocrystalline torsion rocker as is known from Z. Kadar, A. Bossche and J. Mollinger, Integrated Resonant Magnetic Field Sensor, Sensors and Actuators A, 41-42, (1994), pp. 66-69.
This magnetic field sensor is composed of a monocrystalline rocker structure suspended on torsion bars, printed circuit traces of aluminum being deposited on the structure. As before, an alternating current having the resonant frequency of the mechanical torsional vibrator is sent through the printed circuit trace. A vibrational amplitude (angle of torsion) arises which is read out capacitively via separate electrodes. The counter-electrode is formed by a patterned, conductive layer, which is deposited on a glass cap having depressions (cavities). The resonant method and the low "structural attenuation" of the vibrator supposedly make it possible to measure magnet fields in the nT range due to a possible vacuum enclosure and the resulting high qualities. In addition, a large dynamic range is indicated by the authors. Feedback printed circuit traces and a synchronous detector (carrier-frequency method) are used for the capacitive readout. The sensor design approach implemented in the laboratory has rest capacities in the range of 0.5 pF. The corresponding manufacturing process is hardly suited for inexpensive series production due to the complicated (and expensive) process steps. This publication does not reveal how the described crossover of printed circuit traces is implemented.
The third known magnetic field sensor structure is a non-resonant design approach, in which a direct current flows through one half of a silicon rocker structure (no separately applied printed circuit traces), the direct current interacting with the magnetic field and producing a Lorentz force. This force is converted into a torsional moment, which then twists the rocker structure. The changes in capacitance of the rocker areas toward the lower-lying counter-electrodes resulting from this torsion are read out using a capacitive method of measurement.
Furthermore, there are magnetic field sensors, which are based on electromagnetic material effects.
For example, the Hall effect is utilized. The Fall effect occurs in current-carrying conductors in the presence of an external magnetic field. The electrons are deflected perpendicularly to their moving direction depending on the current-carrying material. This deflection produces a potential difference between the two sides of the conductor, the potential difference representing the measured Hall effect. The following disadvantages can be enumerated regarding Hall-effect sensors: highly limited resolution (usual resolution limits lie in the mT range), a highly limited dynamic response, a great offset and a high temperature dependence of the measured effect.
Other sensors, which are based on electromagnetic material effects, include magnetoresistive sensors, in which the electrical resistance increases in the presence of a magnetic field (see, for example, M. J. Caruso, Applications of Magnetoresistive Sensors in Navigation Systems, 1997 Society of Automotive Engineers, Inc., Publ. # 970602, pp 15-21).
Fluxgate sensors, in which the sensor and the electronic unit are usually provided on one chip, some of them having a high resolution of typically 9 mV/.mu.T, were disclosed, for example, by R. Gottfried--Gottfried, W. Budde, R. Jahne, H. Kuck, B. Sauer, S. Ulbricht and U. Wende, A Miniaturized Magnetic Field Sensor System Consisting Of A Planar Fluxgate Sensor And A CMOS Readout Circuitry, Sensors and Actuators A54 (1996), pp. 443-447.
With regard to the above known approaches it turned out to be disadvantageous that the magnetic field sensors have either a low resolution, i.e., sensitivity, or a high-temperature-dependent offset, or that their production is very costly.